The human body is a finely tuned system, with the nervous and digestive systems closely intertwined. At the center of this connection lies the vagus nerve—a long, wandering cranial nerve that plays a critical role in regulating internal organ function, including digestion. Chronic stress, unfortunately, can disrupt this delicate balance, leading to a range of digestive problems. Understanding how stress affects the vagus nerve offers insight into the root causes of gastrointestinal (GI) issues and how to potentially manage them.

What Is the Vagus Nerve?

The vagus nerve is the tenth cranial nerve and one of the most important components of the parasympathetic nervous system—the part responsible for “rest and digest” functions. It extends from the brainstem all the way down to the abdomen, innervating major organs such as the heart, lungs, and most of the digestive tract. It helps regulate heart rate, breathing, and the secretion of digestive enzymes and bile.

Importantly, about 80% of vagus nerve fibres are afferent, meaning they carry information from the body to the brain. This makes it a major communication pathway between the gut and the brain, often referred to as the gut-brain axis.

How Stress Affects the Vagus Nerve

When the body perceives a threat, it activates the sympathetic nervous system, triggering the “fight or flight” response. This leads to increased heart rate, elevated blood pressure, and the release of stress hormones like cortisol and adrenaline. While these reactions are adaptive in the short term, chronic stress can inhibit the function of the vagus nerve.

1. Reduced Vagal Tone

Vagal tone refers to the activity of the vagus nerve. High vagal tone is associated with strong parasympathetic activity, helping maintain digestive motility, secretion of digestive juices, and a calm, regulated nervous system. Chronic stress can lower vagal tone, impairing the nerve’s ability to send calming signals to the gut. This may lead to sluggish digestion or spasms.

2. Inflammatory Response

Stress-induced inhibition of the vagus nerve also weakens its anti-inflammatory effects. The vagus nerve normally helps regulate immune response and inflammation through the “cholinergic anti-inflammatory pathway.” When this function is compromised, inflammation in the gut can increase, contributing to disorders like irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD).

3. Altered Gut Motility and Secretions

Under stress, the vagus nerve reduces signalling to the stomach and intestines. This can cause delayed gastric emptying (gastroparesis), bloating, constipation, or diarrhoea. It also affects the release of digestive enzymes and bile, impairing nutrient absorption and digestion.

Common Digestive Issues Linked to Vagal Dysfunction

• Irritable Bowel Syndrome (IBS): Characterised by abdominal pain, bloating, constipation, or diarrhoea, often worsened by stress.
• Gastroparesis: A condition involving delayed stomach emptying, leading to nausea, vomiting, and fullness.
• Leaky Gut (Intestinal Permeability): Chronic stress may contribute to the breakdown of the gut lining, allowing undigested food and toxins into the bloodstream.
• Acid Reflux (GERD): Impaired vagal function can lead to poor sphincter control at the stomach entrance, allowing acid to reflux into the oesophagus.

Supporting Vagal Health to Improve Digestion

While reducing stress is easier said than done, various practices can help support vagal tone and, in turn, digestive health:

• Deep Breathing and Meditation: Activate the parasympathetic nervous system through slow, diaphragmatic breathing.
• Cold Exposure: Brief exposure to cold (e.g., cold showers or face splashing) can stimulate vagal activity.
• Singing, Humming, and Gargling: These activities stimulate the vagus nerve via muscles in the throat and vocal cords.
• Regular Exercise: Especially low-intensity aerobic activities like walking or yoga.
• Gut-Friendly Diet: A diet rich in fibre, fermented foods, and polyphenols supports a healthy microbiome, which communicates with the vagus nerve.

Final Thoughts

The vagus nerve is a key player in the communication between the brain and the gut. Chronic stress disrupts this communication, leading to a cascade of digestive issues. By understanding this connection, individuals suffering from stress-related GI symptoms can explore holistic approaches to improve vagal tone and restore digestive balance. Managing stress is not just about mental health—it’s vital for gut health too.